This invention pertains to the radio communication art and, more particularly, to a means for monitoring and controlling the power developed by a radio transmitter.
The prior art has developed numerous means for monitoring and controlling the output of radio frequency transmitters to a preset level. The need for such means is a result both of governmental controls regulating the maximum output of transmitters as well as a manufacturer's requirement that each transmitter he produces is capable of producing a given power level.
Two methods are normally used to sense the forward power developed by the transmitter. In one method, sensing current limiting to the final stage of the transmitter is employed. In the other, forward power out of the amplifier is sensed.
Also, techniques have been developed for monitoring the temperature of the transmitter output stage, and reducing the output power level if the sensed temperature exceeds a predetermined limit.
Prior art transmitter power control circuits which employ power limiting and thermal sensing have not proven to be precise in operation. In addition, they have become very complex and specialized working over a narrow power and/or frequency range. This, basically, due to the fact that prior art circuit configurations for limiting power output, and sensing output stage operating temperature have also been sensitive to unrelated circuit parameters such as circuit component values, bias voltages and output load variations. The lack of precision in prior art transmitter power control circuits has resulted in transmitters which either cannot produce or maintain their rated power, or generate in excess of their allowed power level.